Blot the moisture from the roast with paper towels. Heat up a Dutch oven over a medium-high flame. Brown the loin in peanut oil, discarding the excess grease. Add wine, tomatoes, diced onions, garlic, mushrooms, and cayenne pepper. Season with salt and pepper to taste. Bring contents to a rolling boil, cover, cut the heat to a slow simmer, and braise for 1 1/2 hrs. Periodically, turn the loin and stir the sauce.
Remove loin from pan and place it into a platter. Tighten up the sauce with some of the roux. Wisk the roux, bit by bit, into the sauce until it takes on a shimmer, but do not overly firm it up. Serve with a rice pilaf. Ladle the sauce over the loin and the rice.